The present invention relates to photographic processing compositions, in particular a partially oxidized polyalkyleneimine antioxidant for use in photographic developer that is as stable as present systems and odour-free.
The fundamental step of photographic processing is development. Development is carried out using a developing agent. The developing agent reduces silver halide to form silver. This silver gives the black-and-white image. The developing agents are oxidized by oxygen in the air and conventionally an antioxidant is added to the developer to reduce this unwanted reaction.
The fundamental steps in colour photographic processing include a colour developing step and a silver removal step. In the colour developing step, photographic colour developing compositions are used to process colour photographic materials such as colour photographic films and papers to provide the desired colour images. Such compositions generally contain colour developing agents, for example, 4-amino-3-methyl-N-(xcex2-methane sulfonamidoethyl)aniline and other p-phenylenediamines, as reducing agents to react with exposed silver halide to form oxidized colour developer as well as silver. The oxidized colour developer goes on to react with suitable colour forming couplers in the colour photographic materials to form the desired dyes. However, such colour developing agents are susceptible to oxidation by dissolved oxygen from the air and an antioxidant is conventionally included in the colour developer compositions to preserve the oxidation state of the colour developing agent and thereby maintain useful colour developer activity.
Developing compositions are carefully formulated with various additives to overcome various problems besides the problems arising with developing agent oxidation. Thus, metal ions, various sequestering agents, surfactants and other components have been added over the years to provide the stability and photographic activity that is critical to the industry.
Current colour paper developers are often stabilized against aerial oxidation by the inclusion of an antioxidant, N, N diethylhydroxylamine, (hereinafter DEHA), which may work by reducing any 4-(N-ethyl-N-2-methane-sulfonylaminoethyl)-2-methylphenylenediamine sesquisulfate (Kodak Colour Developing Agent CD3, hereinafter CD3) that is oxidized by air and by reacting with dissolved oxygen directly. This particular antioxidant compound has some problems associated with it, for example, it is volatile and produces an unpleasant smell in use.
U.S. Pat. No. 4,252,892 teaches the use of alkyleneimine polymers, especially ethyleneimine polymers, also known as polyethyleneimines, as antioxidants in a colour developer composition. While polyethyleneimines work well after a time, initially there is a rapid loss of colour developing agent.
U.S. Pat. No. 5,466,565 teaches the use of polymeric hydroxylamines as antioxidants in a colour developer composition. The generation of these hydroxylamines from polyalkyleneimines by their reaction with quantitative amounts of hydrogen peroxide at elevated temperatures is described.
There remains a need for a suitable chemical solution developer that provides stability that equals or is better than the current system used and that is odour-free.
It has been found that only partial oxidation is necessary at room temperature to get good antioxidant effects from a polyalkyleneimine. This is a less expensive alternative, is easier to carry out, requires less energy, and in principle, would give more antioxidant effect for a given weight of material, resulting in an antioxidant with a longer life.
The present invention relates to a developer comprising a developing agent and a polyalkyleneimine antioxidant being formed by the condensation of a number of alkyleneimine units and having the following formula (I): 
wherein R1, R2 and R3 independently represent an unsubstituted or substituted alkylene group or R2 may be H;
x and y independently represent an integer from 1 to 39,999;
the sum of x and y represents an integer from 10 to 40,000; and
wherein the amine groups of the antioxidant have been partially oxidized with hydrogen peroxide or a compound capable of generating hydrogen peroxide, prior to the introduction of the developing agent.
In a preferred embodiment, the antioxidant has been partially oxidized such that the amount of hydroxylammonium groups formed is less than half, preferably less than a quarter, the total equivalent of the amine groups of the antioxidant before the addition of the developing agent. In another preferred embodiment, the developer further comprises an alkaline buffer. Preferably the developer is a colour developer comprising a colour developing agent.
The present invention includes several advantages, not all of which are incorporated in a single embodiment. The developer of the present invention equals or is better than one of the current systems used with respect to solution stability and pH stability. The developer of the present invention is an odour-free developer and is no more expensive to manufacture than current developers, when made on a large scale. The developer of the present invention also has very similar sensitometric effects to the current antioxidant, DEHA. In addition, the developer of the present invention has a similar effect on sensitometry as a solution free of antioxidant. The latter allows for more efficient use of silver in paper, which can result in a capability to make a paper that is cheaper to manufacture. The developer of the present invention comprises a polyalkyleneimine antioxidant, especially a polyethyleneimine antioxidant, (hereinafter EIP), that is environmentally acceptable and is not likely to pose a significant risk to health.